Silver is the most versatile offensive weapon against the supernatural. Where salt and iron handle ghosts, silver is the go-to for solid, physical monsters. Werewolves, shapeshifters, skinwalkers, vetalas, pishtacos, and numerous other creatures are vulnerable to silver. A hunter who does not carry a silver blade and silver ammunition is unprepared for most field encounters.
Usage
Silver bullets are the standard ammunition for monster hunting. Most hunters keep at least one firearm loaded with silver rounds at all times. Silver knives and silver-plated blades serve for close combat. Silver can also be used for detection — some creatures react to silver contact with visible burns or discomfort, which can confirm a suspected creature's nature before combat.
The silver must be relatively pure to be effective. Silver-plated objects work but are less reliable than solid silver. Sterling silver (92.5% silver) is sufficient for most purposes.
Real-World Basis
Silver's association with supernatural protection dates back millennia. Silver is associated with the moon in many traditions (hence the werewolf connection), and the moon has long been linked to madness, transformation, and supernatural activity. Silver's antimicrobial properties — genuinely effective at killing bacteria — may have contributed to its reputation as a "pure" metal with cleansing properties. In alchemy, silver was associated with the feminine, the lunar, and the reflective (mirrors were historically made with silver, and mirrors reveal truth). The silver bullet as a specific werewolf-killer is primarily a modern invention, popularized by 19th and 20th century fiction, but silver's broader protective associations are ancient.